docs: def entropy_H(self, data):
          """Calculate the entropy of a chunk of data."""
          
          if len(data) == 0:
              return 0.0
          
          occurences = array.array('L', [0]*256)
          
          for x in data:
              occurences[ord(x)] += 1
          
          entropy = 0
          for x in occurences:
              if x:
                  p_x = float(x) / len(data)
                  entropy -= p_x*math.log(p_x, 2)
          
          return entropy